Syngas Produced By Plasma Gasification

ABSTRACT

A syngas stream composition comprising on a dry basis up to about 50,000 mg/Nm 3  particulates; 5-39 vol % H 2 ; 5-39 vol % CO; 15-50 vol % CO 2 ; 8-30 vol % N 2 , 0-2 vol % Argon; and 15-50 vol % moisture on a wet basis. The stream includes a H 2 /CO ratio that is about 0.3-2 and at least 15 wt % of particulates have an aerodynamic particle diameter of less than or equal to 1 micron. A gasified waste stream and a method for forming a gasified waste stream are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Application No. 61/412,078,filed on Nov. 10, 2010. The disclosure of Application No. 61/412,078 ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention is directed to a process and system for thegeneration and treatment of syngas. In particular, the presentdisclosure is directed to a syngas stream and a method for producing asyngas stream produced by the plasma gasification of waste, includingmunicipal solid waste (MSW).

The effective management and utilization of waste is a global issue.Current waste management techniques, as suggested by regulatoryagencies, such as the Environmental Protection Agency (EPA), includesource reduction first, recycling and composting second, and, finally,disposal in landfills or waste combustors. Other techniques of managingwaste include converting the waste to energy involving processes such asincineration and pyrolysis. There are many types of waste includingmunicipal solid waste, commercial and industrial waste, construction anddemolition waste, solid recovered fuel (SRF), refuse derived fuel (RDF),sewage sludge, electronic waste, medical waste, nuclear waste, andhazardous waste. Municipal solid waste (MSW), also called urban solidwaste, trash, rubbish, or garbage, mainly comprises household/domesticwaste. MSW is generally in solid/semi-solid form and includes paper andcard, plastic, textiles, glass, metals, biodegradable waste (kitchenwaste, yard sweepings/trimmings, wood waste), inert waste (dirt, rocks)and may include small quantities of miscellaneous materials such asbatteries, light bulbs, medicines, chemicals, fertilizers, etc.Typically MSW is found to be predominantly paper/card and kitchen waste,although exact compositions can vary from one region to anotherdepending upon the degree of recycling done by households and transferstations and/or processing facilities.

One form of waste management includes gasification. Gasification is aprocess for the conversion of a carbonaceous feedstock such as coal,petroleum, biofuel, biomass, municipal solid waste (MSW), and otherwastes into a combustible gas such as synthesis gas. Synthesis gas,commonly referred to as syngas is a mixture of varying amounts of carbonmonoxide and hydrogen (CO+H₂) and has a variety of applications. Thesyngas can be used to generate power by combusting directly in a gasturbine, boiler or reciprocating engine and waste heat can be used inthe generation of steam which can provide additional power through asteam turbine. Syngas can also be used for the production of hydrogen orliquid fuels or chemicals, which may be used as raw materials in themanufacture of other chemicals such as plastics. Gasification is thus aprocess for producing value added products and/or energy from organicmaterials. Typical gas compositions from the gasification of variouspredominantly carbon-based feedstocks in oxygen are presented in Table1.

TABLE 1 Representative Syngas Compositions from the Gasification ofVarious Predominantly Carbon-Based Feedstocks Natural Gas AsphalteneCoal Pet Coke vol % dry vol % dry vol % dry vol % dry gas, O₂ gas, O₂gas, O₂ gas, O₂ fired fired fired fired H₂ (v/v %) 63.0 44.7 38.0 33.0CO (v/v %) 33.5 45.0 45.0 53.2 CO₂ (v/v %) 3.0 10.0 15.0 12.0 N₂ (v/v %)0.2 0.3 2.0 0.6 CH₄ (v/v %) 0.3 500 ppm 250 ppm 0.2 H₂S (ppm) 0 1.3 0.91.5 H₂/CO 1.8 1.0 0.9 0.6

Current waste management techniques, for example as suggested by theEPA, include source reduction first, recycling and composting second,and, finally, disposal in landfills or waste combustors. Othertechniques of managing waste include converting the waste to energyusing processes such as incineration or pyrolysis. Gasification variesfrom these processes in that it involves controlled oxygen levels andtemperatures in the gasifier, thereby leading to a gas stream richer insyngas.

A particular form of gasification includes plasma gasification. Plasmagasification is a waste treatment technology that uses electrical energyand the high temperatures created by a plasma arc to break down wasteinto a gaseous product which contains syngas and molten, glass-likeby-product (slag) in a vessel called the plasma gasification reactor.Plasma is a high temperature luminous gas that is partially ionized andis made up of gas ions, atoms and electrons. Slag is produced from thevitrification of inorganic mineral matter such as glass and metals whichare often contained in waste. Depending on the composition of the MSWand the gasification process, the volatiles typically comprise CO, H₂,H₂O, CO₂, N₂, O₂, CH₄, H₂S, COS, NH₃, HCl, Ar, Hg, HCN, HF, saturatedand unsaturated hydrocarbons (tars) and char (ash).

Whether the purpose of producing syngas is to generate electricity or toproduce chemicals, the various impurities present in the raw gas fromthe gasifier need to be removed prior to usage. The extent of theirremoval and that of the other components is highly dependent upon thenext steps to create a useful product, with very specific requirementsneeded to maximize the generation of power.

One known process for gasification of municipal solid waste (MSW) aswell as other biomass such as wood is disclosed by Faaij et. al. inBiomass and Bioenergy, 12(6), 387-407 (1997), hereinafter “the Faaijreference”. The compositions disclosed in the Faaij reference representair-fired gasification of MSW and other biomass. However, the crudesyngas of Faaij contains 13.98 v/v % CO in wet syngas (16 v/v % CO indry gas), which is undesirably low compared to desired syngascomposition from waste gasification systems. The Faaij referenceincludes processes that are limited only to air-fired gasification. Inaddition, the Faaij reference utilizes a specific type of circulatingfluidized bed (ACFB type) gasifier from TPS Technology. In addition, theFaaij reference does not disclose COS or HCl as part of the syngas. TheNH₃ concentration in the Faaij reference is disclosed as 1.00 v/v % (wetbasis), corresponding to 11,700 ppm NH₃. In addition to the otherdrawbacks above, the concentration of NH₃ in Faaij is undesirably highfor known waste gasification and cleanup systems.

Another known syngas production method is disclosed by M. Morris et al.of TPS Termiska Processer AB, NykoEping, Sweden in Waste Management.1998, 18 (6-8), 557-564, hereinafter “the TPS Termiska reference” wherethe composition of syngas produced from MSW and biomass has beenprovided. As in the case of the Faaij reference, the CO concentration isundesirably low for conventional waste gasification and cleanup systems.The composition of CO in the syngas stream disclosed in the TPS Termiskareference is 8.8 v/v % in wet gas (9.74 v/v % in dry gas) and 48 ppm ofH₂S. The TPS Termiska reference does not disclose COS, HCl, NH₃ or HCN.As in the case of the Faaij reference, the TPS Termiska reference doesnot disclose a plasma gasifier, but is limited to a circulatingfluidized bed gasifier. In addition, the TPS Termiska reference islimited to air-fired gasification. In addition to the above drawbacks,the TPS Termiska reference requires pre-sorting and processing of MSWprior to gasification, increasing cost and energy requirements.

Another known gasification process is disclosed by Jae Ik Na et. al. inApplied Energy, 2003, 75, 275-285, hereinafter “the Jae Ik Nareference”. The Jae Ik Na reference discloses gasification of MSW in afixed bed gasifier. FIGS. 9 and 10 in the Jae Ik Na reference disclose aCO₂ composition of 20-60% and 5-20% CH₄, in the syngas, which isundesirably high, thereby leading to higher costs due to specialprocesses associated with removal of these species. The Jae Ik Nareference does not disclose N₂, H₂S, COS, HCl, NH₃, HCN or hydrocarbonsother than CH₄. In addition, the Jae Ik Na reference does not disclose aparticulate loading. In addition, the fixed bed gasifier of the Jae IkNa reference involves drying, pyrolysis, gasification and combustionzones within the gasifier, wherein, each zone requires differenttemperatures, providing for complicated processing and additionalcontrol and/or energy consumption.

A known plasma gasification process is disclosed by a publication M.Minutillo et. al. of University of Cassino, Italy in Energy Conversionand Management 50 (2009) 2837-2842, hereinafter “the University ofCassino reference”. The University of Cassino reference disclosesinformation on syngas produced by plasma gasification of refuse derivedfuel (RDF). The amount of CO, therefore reducing the H₂/CO ratio,disclosed in the University of Cassino reference is undesirably high forconventional waste gasification and cleanup systems. Additionally, theUniversity of Cassino reference does not indicate a syngas compositionfrom MSW. Instead their research involves use of refuse derived fuel(RDF) which is created from MSW by sorting and processing to eliminateas much noncombustible material as possible, thereby significantlyincreasing the cost and energy associated with the process.

Another plasma gasification process is described in a publication byVaidyanathan et. al. in Journal of Environmental Management 82(2007)77-82, hereinafter “the Vaidyanathan reference”. The Vaidyanathanreference discloses plasma gasification of industrial waste and solidwaste from the U.S. army. The Vaidyanathan reference does not disclosehydrocarbons, HCl, NH₃, HCN, H₂₅ and COS concentrations or particulateloads. In the Vaidyanathan reference, a surrogate solid waste stream isformed to mimic the U.S. army waste stream in their laboratorygasification experiments. The composition of the solid waste streamreported in the Vaidyanathan reference is very different than typicalMSW compositions. For example, the paper and card content is about 55 wt% which is much higher than the typical range of 10-35 wt %. Plasticcontent of the U.S. Army waste is at 25 wt % which is also significantlyhigher than the typical range of 5-15 wt % in typical MSW.

U.S. Pat. No. 6,987,792 discloses a syngas composition with at least40-45% H2 and at least 40-45% CO, but fails to disclose any othercomponents.

In addition to the chemical makeup of the syngas, the quality of thesyngas stream is addressed in terms of particulate loading anddistribution of particulate sizes. More specifically, the twoparticulate properties for measuring the quality of a syngas streaminclude the particulate loading and the percent particulate below 1micron. As one skilled in the art of particulate removal wouldappreciate, particulates below 1 micron become increasingly difficult toremove. As such, concentrations and/or amounts of particulate below 1micron provide a measure of the ease or difficulty in which the processstream can be treated.

Examples of particulate loading and sizes are disclosed by the EPA'sEmission Standards and Engineering group, who released a two volumereport entitled “Control Techniques for Particulate Emissions fromStationary Sources”, hereinafter, the EPA Report. The EPA reportprovides examples of particulate and size distributions for variousindustrial applications. Two illustrative applications will be drawnforth for discussion from the incineration of MSW. The first instructiveexample utilizes the particulate loading and particle size distributiondata provided for a typical large scale, stoker like, MSW furnaceburning roughly 38,200 kg/hr of solid waste. The furnaces referenced aretypical of those built in Europe in the 1940's with five or six inoperation in the US in 1982, the year the report was issued. The resultsshow uncontrolled particulate matter (PM) emissions, the particulatespresent in the stream prior to particulate clean up, having a loading of2,360 mg/Nm³ and a particle size distribution of less than 20 wt % beingsmaller than 1 micron in size. Conversely, a second example for asmaller modular system with a staged combustion approach to incinerationof MSW yielded particulate loading much higher in small particulates,with greater than 90 wt % of the PM emissions being below 1 micron, withsimilar loadings of 180-3,340 mg/Nm³. The EPA reports also detailsparticulate loading and particle size distribution for blast furnaceoffgas. The gas is produced in the making of pig iron and produces a topgas rich in particulate, 27,500 mg/Nm³, in which less than 10 wt % ofthe particulate is less than 74 microns. Syngas and off gas compositionshaving high particle loadings and high concentrations of fineparticulates below about 1 micron are generally not known in the art.What is desired in the art is a high quality syngas composition formedfrom gasified waste or plasma gasified waste, that is suitable forefficient cleanup and energy production and does not suffer from thedrawbacks of the prior art.

BRIEF SUMMARY OF THE INVENTION

One aspect of the disclosure includes a syngas stream compositioncomprising up to about 50,000 mg/Nm³ particulates, 5-39 vol % H₂, 5-39vol % CO, 15-50 vol % CO₂, 10-60 vol % N₂, and 0-2 vol % Argon on a drybasis; and 15-50 vol % moisture on a wet basis. The stream includes aH₂/CO ratio that is about 0.3-2.0 including at least 15 wt % of theparticulates have an aerodynamic particle diameter of less than or equalto 1 micron.

Another aspect of the disclosure includes a syngas stream compositioncomprising between about 5,000 and 29,500 mg/Nm³ or between about 30,500and about 50,000 mg/Nm³ particulates, 10-30 vol % H₂, 15-39 vol % CO,15-35 vol % CO₂, 10-30 vol % N₂, and 0-2 vol % Argon on a dry basis; and15-30 vol % moisture on a wet basis. The stream includes a H₂/CO ratiothat is about 0.6-1.5 including at least 15 wt % of the particulateshave an aerodynamic particle diameter of less than or equal to 1 micron.

Another aspect of the disclosure includes a syngas stream compositionobtained by oxygen-fired gasification comprising up to about 50,000mg/Nm³ particulates, 5-39 vol % H₂, 5-39 vol % CO, 15-50 vol % CO₂, 8-30vol % N₂, and 0-2 vol % Argon on a dry basis; and 15-50 vol % moistureon a wet basis. The stream includes a H₂/CO ratio that is about 0.3-2.0including at least 15 wt % of the particulates have an aerodynamicparticle diameter of less than or equal to 1 micron.

In another embodiment of the invention, on a dry basis the syngas streamcomposition arising from oxygen fired gasification comprises betweenabout 5,000 and 29,500 mg/Nm³ or between about 30,500 and 50,000 mg/Nm³particulates, 10-35 vol % H2, 15-39 vol % CO, 15-40 vol % CO2, 8-15 vol% N2, and 0-2 vol % Argon; and 15-30 vol % moisture on a wet basis. Thestream includes a H2/CO ratio that is about 0.6-1.5 and at least 15 wt %of the particulates have an aerodynamic particle diameter of less thanor equal to 1 micron.

Another aspect of the disclosure includes a syngas stream includinggasified waste composition arising from oxygen-fired gasificationcomprising up to about 50,000 mg/Nm³ particulates, 5-39 vol % H₂, 5-39vol % CO, 15-50 vol % CO₂, 8-30 vol % N₂, and 0-2 vol % Argon on a drybasis; including 15-50 vol % moisture on a wet basis. The streamincludes a H₂/CO ratio that is about 0.3-2.0 and at least 15 wt % of theparticulates have an aerodynamic particle diameter of less than or equalto 1 micron.

In another embodiment of the invention, on a dry basis the gasifiedwaste composition arising from oxygen-fired gasification that comprisesbetween about 5,000 and 29,500 mg/Nm³ or between about 30,500 and 50,000mg/Nm³ particulates, 10-35 vol % H2, 15-39 vol % CO, 15-40 vol % CO2,8-15 vol % N2, and 0-2 vol % Argon and 15-30 vol % moisture on a wetbasis. The stream includes a H2/CO ratio that is about 0.6-1.5 and atleast 15 wt % of the particulates have an aerodynamic particle diameterof less than or equal to 1 micron.

Another aspect of the disclosure includes a syngas stream including theplasma gasified waste composition arising from oxygen-fired gasificationcomprising up to about 50,000 mg/Nm³ particulates, 5-39 vol % H₂, 5-39vol % CO, 15-50 vol % CO₂, 8-30 vol % N₂, and 0-2 vol % Argon on a drybasis; and 15-50 vol % moisture on a wet basis. The stream includes aH₂/CO ratio that is about 0.3-2 and at least 15 wt % of the particulateshave an aerodynamic particle diameter of less than or equal to 1 micron.

In another embodiment of the invention, on a dry basis the plasmagasified waste composition arising from oxygen-fired gasificationcomprises between about 5,000 and 29,500 mg/Nm³ or between about 30,500and 50,000 mg/Nm³ particulates, 10-35 vol % H2, 15-39 vol % CO, 15-40vol % CO2, 8-15 vol % N2, and 0-2 vol % Argon; and 15-30 vol % moistureon a wet basis. The stream includes a H2/CO ratio that is about 0.6-1.5and at least 15 wt % of the particulates have an aerodynamic particlediameter of less than or equal to 1 micron.

Another aspect of the present disclosure is a method for generating asyngas composition of the invention via the plasma gasification ofwaste. Without wishing to be bound by any theory or explanation, it isbelieved that the composition of the inventive syngas can vary dependingupon the composition of the waste employed, the amount of oxygen presentduring gasification, and the temperature within the gasifier. Ingeneral, the higher operating temperature of the plasma gasifier allowsfor a wide range of feedstocks to be used while producing well-definedsyngas compositional ranges. The use of oxygen during gasification canbe varied in order to maximize the energy value of the syngas fromhighly variable waste while maintaining a relatively consistent syngascompositional range For example, increasing the amount of oxygen presentduring plasma gasification (or using an oxygen-fired gasification) canproduce a syngas having increased CO₂ levels and lower N₂ levels. Forthe purpose of this invention, the term “oxygen-fired” means that oxygenis introduced into the plasma gasifier for the purpose of aiding inefficiently converting waste into syngas and for improving the energycontent of the syngas and, if desired, may used in combination withoxygen and/or air being introduced into the plasma torch or as a shroudaround the plasma torch. Oxygen can be introduced into the gasifier asoxygen enriched air or as commercial grade oxygen (e.g., at least about90 percent purity (mass basis) oxygen). As a representative but notlimiting example, the concentration of oxygen in the gasifier couldrange from about 1 to about 50 percent by mass.

Another aspect of the present disclosure includes a plasma gasifiedsyngas stream arising from oxygen-fired gasification comprising on a drybasis, up to about 50,000 mg/Nm³ particulates, 5-39 vol % H₂, 5-39 vol %CO, 15-50 vol % CO₂, 8-30 vol % N₂, 0-2 vol % Argon, 1000-5000 ppm HCl,1000-5000 ppm NH₃; 15-50 vol % moisture on a wet basis, and a H₂/COratio that is about 0.3-2.

Another aspect of the present disclosure includes a plasma gasifiedsyngas stream arising from oxygen-fired gasification comprising on a drybasis, between about 5,000 and 29,500 mg/Nm³ or between about 30,500 and50,000 mg/Nm³ particulates, 10-35 vol % H₂, 15-39 vol % CO, 15-40 vol %CO₂, 8-15 vol % N₂, 0-2 vol % Argon, 1000-5000 ppm HCl, 1000-5000 ppmNH₃;15-30 vol % moisture on a wet basis, and a H₂/CO ratio that is about0.6-1.5.

Another advantage of embodiments of the present disclosure is that thewaste may be efficiently gasified to form a high quality syngas using aplasma gasifier.

Still another advantage of embodiments of the present disclosure is theunique combination of high particulate load, HCl concentration and NH₃concentration that permit efficient cleanup of the crude syngas.

Still another advantage of embodiments of the present disclosure is thehigh H₂/CO ratio present in the syngas composition.

Still another advantage of embodiments of the present disclosure is thatthe waste may be controllably and efficiently gasified in the presenceof oxygen.

Still another advantage of embodiments of the present disclosureincludes shredding of waste without sorting prior to gasification, whichreduces or eliminates the need to pre-sort or process waste prior togasification, which may decrease the cost and energy requirements forthe system.

Still another advantage of embodiments of the present disclosureincludes a plasma gasifier that does not require drying, pyrolysis,gasification and combustion zones within gasifier, each zone requiringdifferent temperatures, providing for greater simplification of controlsand equipment.

The various aspects, embodiments, features and advantages can beemployed alone or in combination with each other. Other features andadvantages of the present invention will be apparent from the followingmore detailed description of the preferred embodiment, taken inconjunction with the accompanying drawings which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an exemplary gasification system according to an embodimentof the disclosure.

FIG. 2 shows an exemplary gas treatment system according to anembodiment of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides a high quality syngas composition formedfrom gasified waste or plasma gasified waste that is suitable forefficient cleanup and energy production.

FIG. 1 shows an embodiment according to the present disclosure, whereina treatment system 100 includes a series of systems for gasification ofwaste, removal of impurities, and power generation. The system includesa gasifier 103, a gas treatment system 105, and a power generationsystem 107.

As shown in FIG. 1, the gasifier 103 may be either a plasma or anothertype of gasifier which receives and processes waste feed 111. Conditionsfor the plasma gasification of waste involve high temperatures, areaction vessel slightly above, at, or slightly below atmosphericpressure, and an oxidizer feed 113, such as air and/or oxygen. Whenwaste is utilized as a feed stream, the waste may or may not bepre-sorted prior to gasification to remove recyclable materials such asglass, plastic, and metals, and may be co-fired with highcarbon-containing feedstocks 115, such as coal/metallurgicalcoke/petroleum coke, if desired. Types of waste that may be amenable toa gas treatment process are MSW, commercial waste, industrial waste,construction and demolition waste, solid recovered fuel (SRF), refusederived fuel (RDF), sewage sludge, hazardous waste, automobile shredderresidue, tires, or combinations thereof. In one embodiment, the wastestream that is applicable to this invention may contain up to about40-100 wt % MSW and commercial waste or up to about 40-100% MSW and/orRDF and/or commercial waste, with the remainder of the waste includingindustrial waste, construction and demolition waste, and may includehazardous waste. Less than about 15 wt % industrial waste, less thanabout 30 wt % construction and demolition (C&D) waste and less thanabout 15% hazardous waste may be present.

The composition of the waste fed into the plasma gasifier affects thecomposition of the product syngas stream produced. One of the primarytypes of waste evaluated here is municipal solid waste. Variations inMSW composition significantly alters the composition of the syngasstream produced. The ultimate (i.e. chemical) analysis of various MSWsources was determined and has been reported for various locations.Characterization reports describing the MSW from New York City, overallUS and overall UK suggest MSW compositions such as those shown in Table2.

TABLE 2 Composition of MSW in NYC, US and UK Weight % in MSW ComponentNew York City USA UK Paper and card 31.3 35.7 33.2 Plastic 8.9 11.1 11.2Textile 4.7 4.3 2.1 Glass and metals 9.8 13.4 16.6 Kitchen waste 15 11.420.2 Other Biomass 16 15.9 16.7 Miscellaneous 14.3 8.2 —

MSW may comprise 10-35 wt % paper and card, 5-15 wt % plastic, 2-7 wt %textiles, 2-17 wt % glass and metals, 15-30 wt % kitchen waste, 15-25 wt% biomass (includes yard waste, cut grass, wood chips) and 0-20 wt %miscellaneous other materials such as batteries, household sweepings,tires, rubber and leather (Table 3). Ash accounts for roughly 10-25 wt %of MSW, based on this composition.

TABLE 3 Composition of MSW Component Weight % in MSW Paper and card10-35% Plastic 5-15% Textile 2-7% Glass and metals 2-17% Kitchen waste15-30% Other Biomass 15-25% Miscellaneous 0-20%

In some embodiments, the MSW may be pre-sorted prior to firing in theplasma gasifier and comprises 10-50 wt % paper and card, 0-4 wt %plastic, 2-7 wt % textiles, 0-4 wt % glass/metals, 20-35 wt % kitchenwaste, 15-30 wt % biomass (includes cut grass, wood chips) and 0-20 wt %miscellaneous materials such as batteries and household sweepings, asshown in Table 4.

TABLE 4 Composition of Pre-Processed MSW Component Weight % in MSW Paperand card 10-50% Plastic 0-4% Textile 2-7% Glass and metals 0-4% Kitchenwaste 20-35% Other Biomass 15-30% Miscellaneous 0-20%

The composition of C&D wastes normally includes but is not limited todirt, stones, bricks, blocks, gypsum wallboard, concrete, steel, glass,plaster, lumber, shingles, plumbing, asphalt roofing, heating, andelectrical parts. Yet these materials frequently vary constantly due tothe changing nature of construction materials over time. C&D waste maycontain about 5 to 30 wt % MSW. Overall, C&D waste is composed mainly ofwood products, asphalt, drywall, and masonry; other components oftenpresent in significant quantities include metals, plastics, earth,shingles, insulation, and paper and cardboard.

This invention is based on C&D waste that comprises 10-50 wt % wood,10-60 wt % concrete, 10-30 wt % masonry (bricks, stone, tiles), 5-10 wt% plastic, 5-15 wt % metals, 5-15 wt % paper and card and 0-20 wt %miscellaneous materials such as yard waste (Table 5).

TABLE 5 Composition of C&D Waste Component Weight % Wood 10-50% Concrete10-60% Masonry 10-30% Plastic 5-10% Metals 5-15% Paper and card 5-15%Miscellaneous 0-20%

Commercial waste is similar in composition to MSW and comprises paperand card, plastics, textiles, glass, organic waste, metals and othermaterials. [12] This invention is based on commercial waste thatcomprises 20-70 wt % paper and card, 5-30 wt % plastic, 0-5 wt %textiles, 2-15 wt % glass and metals, 5-15 wt % organic waste (food,garden), and 0-20 wt % miscellaneous materials such as batteries andsweepings (Table 6).

TABLE 6 Composition of Commercial Waste Component Weight % Paper andcard 20-70% Plastic 5-30% Textile 0-5% Glass and metals 2-15% Organicwaste 5-15% Other Biomass 15-25% Miscellaneous 0-20%

The plasma gasification process produces a slag stream 117 with moltenmetals/inorganics from one portion of the plasma gasifier and a productsyngas stream 119 from another portion of the plasma gasifier. By“product syngas stream”, it is meant that the syngas stream is theeffluent of a waste gasification process, such as plasma gasification,and may comprise CO, H₂, H₂O, CO₂, N₂, O₂, CH₄, H₂S, COS, NH₃, HCl, Ar,Hg, C_(x)H_(y), and heavier hydrocarbons (tars), particulates comprisingchar, ash, and/or unconverted fuel.

To provide a support bed for waste and to enable the flow of slag andtransport of gas, optional high carbon-containing feedstocks 115, suchas coke or coal feeds may be provided. Steam 109 may also be added toaid in the transport of gas or the flow of slag or for temperaturemoderation.

Certain embodiments of the present disclosure are directed to thecomposition of a heterogeneous syngas stream produced by the plasmagasification of waste, especially municipal solid waste (MSW) andcommercial waste. The syngas exits the plasma gasifier at hightemperature and is first cooled in the gasifier or in an elbow ductdirectly connected to the gasifier. Cooling in the freeboard region ofthe gasifier may optionally be considered as part of the cooling in thegasifier. The syngas is then cooled further by performing a quench stepalong with particulate and other impurity removal. As it comes out ofthe gasifier, the cooled stream contains several gas-phase components inaddition to CO and H₂ including NH₃, HCl, CO₂, N₂, Ar, COS, H₂S, inerts,water vapor and hydrocarbons. Other impurities present in the gas streaminclude metallic impurities such as mercury and a large amount ofparticulate matter. This invention identifies the composition of the gasstream at the exit of the plasma gasifier. The unique properties of thisstream are important in identifying an appropriate clean-up trainrequired to purify this stream so that the syngas may be utilized forpower generation using a gas turbine, reciprocating engine, or internalcombustion engine. Some unique features of the product syngas stream arethe high particulate content and high concentrations of ammonia and HCl.HCl and ammonia are present in comparable concentrations and therebyallow for unique clean-up technology such as co-scrubbing. The H₂S andCOS compositions also provide a distinctiveness to the gas stream.

As shown in FIG. 1, the product syngas stream 119 is fed to a gastreatment system 105, wherein impurities, such as particulates, tars,HCl, NH₃, water, mercury, H₂S, COS, inerts, hydrocarbons and otherimpurities are removed from syngas to form a clean syngas stream 121. By“clean syngas stream” it is meant that the syngas is sufficiently freeof impurities for use in combustion for power generation, fuel orchemical manufacture, hydrogen production and/or for applications thatutilize CO and/or H₂. In particular, the particulate content of theclean syngas stream 121 is between 1 and 3 mg/Nm³ if fed to a gasturbine for power generation.

The clean syngas stream 121 may be a clean syngas stream for powerproduction, which is fed to a power generation system 107 wherein thesyngas is combusted or otherwise utilized to generate power. In oneembodiment of the invention, the product syngas stream is fed into aclean-up system and power generation system that are designed tomaximize the production of power from gasified waste. In otherembodiments, the power generation system 107 may be replaced with achemical or liquid fuel manufacturing process such as theFischer-Tropsch process, a hydrogen separation unit or series of unitsto produce clean hydrogen, or other unit or device that utilizes syngasfor chemical synthesis or other process that utilizes CO and/or H₂.

FIG. 2 shows a schematic view of the gas treatment system 105 forremoving impurities from product syngas stream 119. Theparticulate-laden product syngas stream 119 from the plasma gasifier 103is cooled in a quench sub-system 201 which is part of the syngastreatment or clean-up system, 105.

An exemplary but not limiting arrangement of plasma gasifier for usewith the present disclosure includes a vessel of a verticalconfiguration, having a bottom section, a top section, and a roof overthe top section. In certain embodiments, the bottom section, which maybe cylindrical, contains a carbonaceous bed into which one or moreplasma torches inject a plasma gas to create an operating temperature ofat least about 600° C. (for example up to about 2000° C.). Although theplasma torches themselves can reach temperatures of about 2000 to about3000° C. or higher, the temperature that the waste or feedstocks aresubjected to can range from about 800 to about 1500° C. range andtemperature of the syngas exiting the gasifier can range in temperatureof about 800 to about 1200° C. The top section extends upward from thebottom section as a conical wall, substantially continuously without anylarge cylindrical or other configured portions, to the roof of thevessel, the conical wall being inversely oriented, i.e., its narrowestcross-section diameter being at the bottom where it is joined with thebottom section, and is sometimes referred to herein as having the formof a truncated inverse cone. United States Patent ApplicationPublication 2010/0199557A1 discloses a plasma gasification reactor, andis hereby incorporated by reference.

One desirable aspect of the invention is that the higher temperaturesemployed for gasification enable a higher percentage of syngas to beproduced per unit waste with less tars and other hydrocarbonsby-products thereby permitting more efficient power production with theresulting syngas. For example, the inventive syngas can contain lessthan about 14% tar and other hydrocarbons.

Another exemplary, but not limiting, arrangement of plasma gasifier foruse with the present disclosure includes a bottom section with a cokebed in which plasma torches and a mix of oxygen/air/steam tuyeres aredirected at the coke bed. Above the bottom section is a lower feed bedsection in which oxygen/air/steam tuyeres are located at least one levelabove the coke bed and where flows are directed at the bed of wastematerial that rests on the coke bed. The lower feed bed section includesside feed ports. Above the lower feed bed section is a freeboard sectionwhich provides residence time for hot gas. Above the freeboard sectionwithin the gasifier is an optional partial cooling section which coolsthe gas via a water only spray, via steam injection, or via acombination of the two. An optional recycle of syngas or other fluid mayalso be used to cool the syngas within the gasifier. Above the partialcooling section in the gasifier is an elbow duct.

The syngas formed by the gasifier has a unique composition of the syngasstream produced by the plasma gasification of waste, especiallymunicipal solid waste (MSW). The syngas exits the plasma gasifier athigh temperatures such as 800-1200° C. (˜1500-2200° F.), and mayoptionally be cooled at the exit of the gasifier to about 1000° C., 900°F., or even 800° F., and is then cooled to much lower temperatures byperforming a quench. Optionally, a radiant cooler may be used for wasteheat recovery.

The product syngas stream from a plasma gasifier processing waste andoperating in the air-fired or oxygen-fired modes, has a temperature ofup to about 1500-2200° F. and can contain up to about 50,000 mg/Nm³ orfrom about 30,500 to 50,000 mg/Nm³ or from 5,000 to 29,500 mg/Nm³particulates. In addition, the particle size distribution of theparticulate matter present in the syngas stream from the gasifierincludes at least 15 wt %, or at least 30 wt %, or at least 50 wt % ofthe particulate having an aerodynamic particle diameter less than orequal to 1 micron. In one embodiment, the plasma gasifier processes awaste stream that comprises of 40-100 wt % MSW and commercial waste,less than about 15 wt % industrial waste, less than about 30 wt %construction and demolition (C&D) waste and less than about 15 wt %hazardous waste and is operated in the air-fired mode. On a dry basis,the gas also comprises 4-39 vol % H₂, 5-39 vol % CO, 15-50 vol % CO₂,10-60 vol % N₂ and 0-2 vol % Argon. The gas stream may contain 15-50 vol% moisture. The H₂/CO ratio is about 0.3-2 as shown in Table 7. Thepost-quench syngas stream is saturated in water.

In another embodiment of the invention, on a dry basis the gas comprises10-30 vol % H2, 15-39 vol % CO, 15-35 vol % CO2, 10-30 vol % N2, and 0-2vol % Argon and the H2/CO ratio is about 0.6-1.5.

In the oxygen-fired mode, the product syngas stream comprises 15-50 vol% moisture. On a dry basis, the gas also comprises 5-39 vol % H₂, 5-39vol % CO, 15-50 vol % CO₂, 8-30 vol % N₂ (due to air ingress) and 0-2vol % Argon. The H₂/CO ratio is about 0.3-2 as shown in Table 7. Thepost-quench syngas stream is saturated in water.

In another embodiment of the oxygen-fired mode, the product syngasstream comprises 15-30 vol % moisture. On a dry basis, the gas alsocomprises 10-35 vol % 15-39 vol % CO, 15-40 vol % CO₂, 8-15 vol % N₂(due to air ingress) and 0-2 vol % Argon. The H₂/CO ratio is about0.6-1.5 as shown in Table 7. The post-quench syngas stream is saturatedin water.

The product syngas stream also includes small amounts of methane andother gaseous hydrocarbons. On a dry basis, 0-10 vol % CH₄ and 0-4 vol %saturated or unsaturated hydrocarbons other than CH₄ may be found. Anyhydrocarbons in the solid phase are likely removed in the quench step.

The crude syngas stream contains between about 1000 and about 3000 ppmor between about 1000 and 5000 ppm HCl and between about 1000 and about3000 ppm or between about 1000 and 5000 ppm NH₃, quantities which arehigher than typically observed in syngas.

Mercury is present in trace quantities in the product syngas stream aswell as the quenched syngas stream. Up to about 250 ppm mercury may bepresent in the streams. Sulfur is present primarily in the form of H₂Sand COS in the syngas stream. Typically about 500-2000 ppm of sulfur isexpected in the product syngas stream. 1-20% of the sulfur is present inthe form of COS while the balance is present as H₂S.

TABLE 7 Crude Syngas Composition from the Gasification of Waste vol %dry vol % dry vol % dry vol % dry gas, Air gas, Air gas, Oxygen- gas,Oxygen- fired fired fired fired H2 (v/v %)  5-39 10-30  5-39 10-35 CO(v/v %)  5-39 10-39  5-39 15-39 CO2 (v/v %) 15-50 15-35 15-50 15-40 N2(v/v %) 10-60 10-30  8-30  8-15 CH4 (v/v %)  0-10  0-10  0-10  0-10CxHy(v/v %) 0-4 0-4 0-4 0-4 H2S (ppm)  400-2000  400-2000  400-2000 400-2000 COS (ppm)  5-400  5-400  5-400  5-400 HCl (ppm) 1000-50001000-5000 1000-5000 1000-5000 NH3 (ppm) 1000-5000 1000-5000 1000-50001000-5000 Ar (v/v %) 0-2 0-2 0-2 0-2 H2/CO 0.3-2  0.6-1.5 0.3-2  0.6-1.5H2O (v/v %) in 15-50 15-30 15-50 15-30 wet gas Particulate Up to 50,000From 5,000 Up to 50,000 From 5,000 matter to 29,500 or to 29,500 or(mg/Nm3) from 30,500 from 30,500 to 50,000 to 50,000

As shown in FIG. 2, a wet quench is done by contacting the productsyngas stream 119 with the quench liquid stream 203, which may includewater, but other solvents can also be used. Quench liquid stream 203 caninclude water at ambient temperature and atmospheric pressure. Thisprocess can be carried out in any appropriate scrubbing equipment anddepending upon the quantity of quench liquid stream 203 input, cansignificantly reduce the gas temperature. For example, a product syngasstream 119 entering the quench sub-system 201 may be at a temperature of1500 to 2000° F. (816 to 1093° C.). The quenched syngas stream 207 maybe at a temperature of less than about 212° F. (100° C.) or from about150° F. (66° C.) to about 200° F. (93° C.) or from about 170° F. (77°C.) to about 200° F. (93° C.). A portion of the particulates, tars orunsaturated hydrocarbons, if present in the gas stream, also are removedin a solid/liquid state in the quench effluent stream 205. The quencheffluent stream 205 may be recycled to the quench liquid stream 203and/or may be flushed with an excess of water and disposed.

Syngas exits the quench step at a temperature depending on the quenchmethodology and operating conditions. The output temperature can bebetween 100° F. (38° C.) and 212° F. (100° C.).

In one embodiment of the present disclosure, the wet quench is performedwith a high volume of water, such as from 200 to 300 m³/h, to allowrapid cooling.

Dioxin and furan formation may occur when process temperatures are inthe range of from about 250° C. (482° F.) to about 350° C. (662° F.) inthe presence of oxygen, when carbon is in the particulates, and when allof these are present at adequate residence time to provide theconditions sufficient to produce dioxin and/or furan. Wet quenching maybe performed under controlled temperatures, such as temperatures below250° C. (482° F.), at residence times and controlled oxygen content toprevent dioxin/furan formation.

In another embodiment of the present disclosure, dry quenching replacesor supplements the wet quenching process. Dry quenching may be performedby evaporative cooling of water at controlled temperatures. In anotherembodiment of the present disclosure, quenched syngas stream 207 can berecycled to exchange heat with the product syngas stream 119 to reducethe gas temperature of the syngas stream 119.

Standard conditions for the plasma gasification of waste involve hightemperatures, a pressure slightly above, at, or slightly belowatmospheric pressure, and air and/or oxygen input to the gasifier. Thewaste may or may not be pre-sorted prior to gasification to removerecyclable materials such as glass, plastic, and metals, and may beco-fired with high carbon-containing feedstocks such coal/metallurgicalcoke/petroleum coke, if needed. As shown in FIG. 1, the process producesa slag stream with molten metals/inorganics at the bottom of the plasmagasifier and a hot syngas stream from the top of the plasma gasifier.The plasma gasifier may be operated in the presence oxygen or air or acombination thereof.

The hot, particle-laden gas from the plasma gasifier is first cooled ina preliminary cooling step which may occur either in the gasifier or inan elbow duct directly connected to the gasifier. The crude, slightlycooled syngas is further cooled in a quench step. As shown in FIG. 2, awet quench is done by contacting the product syngas stream with thequench liquid stream, which may include water, but other solvents canalso be used. The quench liquid stream can include water at ambienttemperature and atmospheric pressure. This process can be carried out inany appropriate scrubbing equipment and depending upon the quantity ofquench liquid stream input, can significantly reduce the gastemperature. For example, a product syngas stream entering the quenchsub-system may be at a temperature of 1500 to 2000° F. (816 to 1093°C.). The post-quenched syngas stream 207 may be at a temperature of lessthan about 212° F. (100° C.) or from about 150° F. (66° C.) to about200° F. (93° C.) or from about 170° F. (77° C.) to about 200° F. (93°C.). A portion of the particulates, tars or unsaturated hydrocarbons, ifpresent in the gas stream, also are removed in a solid/liquid state inthe quench effluent stream 205. The quench effluent stream 205 may berecycled to the quench liquid stream and/or may be flushed with anexcess of water and disposed.

In another embodiment of the invention, dry quenching replaces orsupplements the wet quenching process. Dry quenching may be performed byevaporative cooling of water at controlled temperatures. In anotherembodiment of the invention, cooler downstream syngas can be recycled toexchange heat with the hot syngas to significantly reduce the syngastemperature. In a further embodiment, steam maybe added to the hotsyngas to reduce the syngas temperature.

As shown in FIG. 2, the post-quenched syngas stream 207 is provided tosecondary clean-up train 200, which further processes the post-quenchedsyngas stream 207. Secondary clean-up train 200 may, for example,process the post-quenched syngas stream 207 for use in power generation(see e.g., FIG. 1).

The composition of the syngas was obtained using the results from anin-line Mass Spectrometer and these results were verified by taking bombsamples of the syngas after it exited the gasifier and analyzing themusing Gas Chromatography.

Particulate analyses were carried out per modified EPA Method 5 forParticulate Loading and via GARB 501 for the Particle Size Distribution(PSD).

Particle Loading—Filterable Particulate Matter (FPM)—EPA Method 5(Modified)

Sampling using USEPA Method 5 procedures was modified to collectfilterable particulate matter (FPM) emissions at the approximate syngastemperature, rather than at EPA Method 5 specified 248±25° F. Allsamples were analyzed according to analytical procedure in EPA Method5B; the filters were baked at 160° C.

Particle Size Distribution (PSD)—CARB 501

Particulate matter was withdrawn isokinetically from the source andsegregated by size in an in-situ cascade impactor at the sampling pointexhaust conditions of temperature, pressure, etc. The resulting index ofthe measured particle size is traditionally separated by the particlediameter collected with 50% collection efficiency by each jet stage, andthis diameter is usually called the “cut diameter” and is characterizedby the symbol “D50.” The aerodynamic cut diameter is the diameter of anequivalent unit density sphere which would be collected with 50%efficiency by the specific impactor jet stage. The mass of each sizefraction is determined gravimetrically. Particle size determinationtesting varies from standard mass testing in that too much material canbe collected, voiding the sample, as well as too little material, sothere is no set test length. A target minimum total sample catch of 10milligrams was used, based on the Method 5 (Modified) data. The typicalsample rate for particle sizing is 0.3 to 0.5 cubic feet per minute(cfm).

Example 1

A waste comprising refuse derived fuel was fired in a plasma gasifier inoxygen-fired mode in the presence of metallurgical coke and produces aproduct syngas stream containing 32,000 mg/Nm³ of particulates, 65 wt %of the particles were less than 1 micron in size, at a temperature of1800° F. (982° C.) and a pressure of 0 psig. The concentrations on a drybasis of H₂, CO, CO₂, and N₂ are 28 v/v %, 26 v/v %, 29 v/v %, and 16v/v %, respectively with a moisture content of 20 v/v %. Theconcentrations of NH₃ and HCl are 1800 ppm and 1800 ppm respectively.The crude syngas stream contains 1500 ppm H₂S and 170 ppm COS.

Example 2

A waste comprising refuse derived fuel was fired in a plasma gasifier inoxygen-fired mode in the presence of metallurgical coke and produces aproduct syngas stream containing 28,000 mg/Nm³ of particulates, 35 wt %of the particles were less than 1 micron in size, at a temperature of1800° F. (982° C.) and a pressure of 0 psig. The concentrations on a drybasis of H₂, CO, CO₂, and N₂ are 17 v/v %, 17 v/v %, 38 v/v %, and 28v/v %, respectively with a moisture content of 22 v/v %. Theconcentrations of NH₃ and HCl are 1800 ppm and 1800 ppm respectively.The crude syngas stream contains 1500 ppm H₂S and 170 ppm COS.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for forming a syngas stream comprising: providing a waste;gasifying the waste in the presence of plasma under oxygen-firedconditions to form a syngas stream comprising on a dry basis: up toabout 50,000 mg/Nm3 particulates; 5-39 vol % H2; 5-39 vol % CO; 15-50vol % CO2; 8-30 vol % N2; 0-2 vol % Argon; and 15-50 vol % moisture on awet basis; and wherein the H2/CO ratio is about 0.3-2 and at least 15 wt% of the particulates have an aerodynamic particle diameter of less thanor equal to 1 micron.
 2. The method of claim 1, further comprisinggasifying waste selected from the group consisting of gasified MSW,gasified commercial waste, gasified construction and demolition waste,gasified industrial waste, gasified hazardous waste and combinationsthereof.
 3. The method of claim 2, wherein in the MSW comprises 10-35 wt% paper and card, 5-15 wt % plastic, 2-7 wt % textiles, 2-12 wt % glassand metals, 15-30 wt % kitchen waste, 15-25 wt % biomass and 0-20 wt %other waste material.
 4. The method of claim 2, wherein the commercialwaste comprises 20-70 wt % paper and card, 5-30 wt % plastic, 0-5 wt %textiles, 2-15 wt % glass and metals, 5-15 wt % organic waste and 15-25wt % other biomass.
 5. The method of claim 1, wherein the compositioncomprises 10-35 vol % H2.
 6. The method of claim 5, wherein thecomposition comprises 15-39 vol % CO.
 7. The method of claim 6, whereinthe composition more comprises 15-40 vol % CO2.
 8. The method of claim7, wherein the composition comprises 8-15 vol % N2.
 9. The method ofclaim 8, wherein the stream comprises 5,000 to 29,500 g/Nm3 or 30,500 to50,000 g/Nm3 particulates.
 10. The method of claim 1, further comprising1000-5000 ppm HCl and 1000-5000 ppm NH3.
 11. The method of claim 1,wherein at least 30 wt % of the particulates have an aerodynamicparticle diameter of less than or equal to 1 micron.
 12. The method ofclaim 1, wherein at least 50 wt % of the particulates have anaerodynamic particle diameter of less than or equal to 1 micron
 13. Amethod for forming a syngas stream comprising: providing a waste;gasifying the waste in the presence of plasma under oxygen-firedconditions to form a syngas stream comprising on a dry basis: up toabout 50,000 mg/Nm3 particulates; 5-39 vol % H2; 5-39 vol % CO; 15-50vol % CO2; 10-60 vol % N2; 0-2 vol % Argon; and 15-50 vol % moisture ona wet basis; and wherein the H2/CO ratio is about 0.3-2 and at least 15wt % of the particulates have an aerodynamic particle diameter of lessthan or equal to 1 micron.